Arrangement for attenuation of the overshoot of current pulses in core memories



J. K. A.. oLssoN.

Oct. 21,1970 3,531,031

' ARRANGEMENT FOR ATTENUATION OF THE OVERSHOOT OF CURRENT PULSES, IN CORE MEMORIES 5 Sheets- Sheet 1 Filed Nov-. 30.: 1967 unit...

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ARRANGEMENT FOR ATTENUATION OF THE OVERSHOOT.

g OEgQURRENT PULSES IN CORE IQHJMORIES Efl ed Nov -lyo, -we? s'sneets-snet a United States Patent 3 537,081 ARRANGEMENT FOR AI'I'ENUATION OF THE OVERSHOOT OF CURRENT PULSES IN CORE MEMORIES Jons Kurt Alvar Olsson, Tullinge, Sweden, assignor to Telet'onaktiebolaget L M Ericsson, Stockholm, Sweden, a corporation of Sweden Filed Nov. 30, 1967, Ser. No. 687,059 Int. Cl. G11c 5/02, 7/02 US. Cl. 340-174 3 Claims ABSTRACT OF THE DISCLOSURE The circuit discloses the use of a transformer to reduce the overshoot signals in a matrix wire of a memory core matrix. The wire is connected between the terminals of a primary and a secondary of a differentially coupled transformer, the primary having its other termnial connected to a current source and the secondary having its other terminal connected to ground.

The present invention refers to an arrangement for attenuation of the overshoot of current pulses which are fed, via a conductor to the cores of a core memory.

In a core memory in order to switch the cores it is necessary to supply current pulses via a conductor to the cores. These pulses must have a definite amplitude. Because of the distributed inductance and the distributed capacity to ground of the conductor overshoots will however appear at the leading and the trailing edges of the pulses. The amplitudes of the overshoots increase as the distance from the pulse source increases and reach their highest values at the opposite terminal of the conductor if this terminal is grounded in a conventional way. The size of the amplitudes of the overshoots depend partly on the total capacity to ground of the conductor, and partly on the potential appearing at the terminal of the conductor situated nearest to the pulse source. In order to decrease the amplitude of the overshoots the pulse source is arranged to supply the primray winding of a transformer, the secondary winding of which is connected to the terminals of the conductor. This implies that the voltage between the terminals of the conductor will be symmetrical to ground potential and the centre point of the secondary winding as well as the centre point of the conductor obtain zero potential. Thus the capacities as well as the potential at the terminal of the conductor is reduced to one half and the overshoot will decrease considerably. At the end of the pulse in the primary winding, a current will however appear in the secondary winding which current is oppositely directed to the current appearing in the secondary winding at the beginning of the pulse. This oppositely directed current can be eliminated by a rectifier if the pulses supplied to the primary winding are of a single polarity. If however pulses supplied to the primary winding are of an alternating polarity this can not be done and a disturbing current will appear in the core memory.

An object of the present invention is to eliminate the oppositely directed current appearing at the end of the pulse. Briefly, the invention contemplates a transformer differentially connected in such a way that one terminal of the primary winding is connected to a current generator for generating current pulses. The secondary winding has its corresponding terminal connected to ground. The matrix wire is connected between the remaining terminals of the primary and secondary windings respectively so that the voltage appearing across the matrix wire owing to its impedance will be symmetrical to ground potential.

The invention will be more fully described by means of two embodiments in connection with the accompanying drawing in which FIG. 1 shows a circuit diagram of "ice a conductor which is directly supplied with a current pulse, FIG. 2 schematically shows the form of the current pulses at different points of the conductor, FIG. 3 shows a circuit diagram of a conductor supplied via a transformer, FIG. 4 shows a circuit diagram of an arrangement according to the invention, FIG. 5 shows a modification of the arrangement according to FIG. 4, FIG. 6 shows another embodiment of an arrangement according to the invention and FIG. 7 shows a voltage diagram of the conditions in the arrangement according to FIG. 6.

In FIG. 1 reference 1 indicates a current pulse generator supplying pulses via a conductor or matrix wire D to cores (not shown) distributed along the matrix wire. The total inductance of the matrix wire is represented by a coil L and its the total capacity to ground is represented by two equal capacitors C at the terminals of the matrix wire. The terminal of the matrix wire D remote from the generator is connected to ground. The amplitude of the overshoots will increase along the conductor and reach its highest value at the grounded terminal as schematically shown in FIG. 2 where the length of the conductor is indicated by reference number 1 and the core situated nearest to the pulse source has the ordinal number 1 and core nearest to the grounded terminal has the ordinal number n. The highest value of the amplitudes depends partly on the potential appearing at the beginning of the matrix wire because of the rise time of the pulse, and partly on the total capacity to ground of the conductor.

In FIG. 3 reference character T indicates a transformer having a primary winding which is connected between a pulse source 1 and ground. The secondary winding is connected to the terminals of a matrix wire corresponding to the matrix wire in FIG. 1 whose inductance and capacity to ground per unit of length is constant. Reference A indicates a point of the matrix wire between which point and one terminal the capacity to ground and the inductance are equal to those between the point and the other terminal. The parts D1, D2 of the conductors have been replaced by their schematic equivalents in the same way as in FIG. 1 whereby the capacity values of the capacitors C1 and the inductance values of the coils L1 are reduced to one half of the values of the capacitor C and the coil L respectively in FIG. 1. When the pulse source emits a pulse, a voltage U appears across the primary winding as well as across the secondary winding which is supposed to have the same number of winding turns. If the capacity to ground per unit of length of the conductor is constant the secondary voltage will however be symmetrical to zero potential. In other words, one terminal of the secondary winding has the potential +U/2 and the other terminal has the potential U/2. This implies that the centre point A will have the potential 0 and the largest overshootings will appear at this point. The amplitude of these overshoots wil be considerably smaller than the amplitude appearing at the grounded terminal of the conductor in FIG. 1 since the voltage drop and the influencing capacity are reduced to one half. The disadvantage of this arrangement known in the prior art is that the secondary winding provides a low ohmic signal which implies that when the pulse in the primary winding ceases a current oppositely directed to the current appearing during the pulse time, is generated in the secondary winding. This oppositely directed current can be eliminated by introducing a rectifier in the secondary circuit if the pulses in the primary winding have a constant polarity. If however the pulses are of an alternating polarity this solution can not be used and the disturbing current can not be eliminated.

In FIG. 4 is shown an embodiment of an arrangement according to the invention in which the components are identical to the components in FIG. 3 and have the same reference characters. As can be seen the transformer is differently connected in such a way that the current pulses are supplied to the conductor via the primary winding and from the matrix wire via the secondary winding to ground. At the start of the pulse the potential U at the input of the primary winding is U in the same way as in FIG. 3. Consequently the potentials of the terminals of the conductor connected to the primary winding and the secondary winding will be +U/2 and -U/2 respectively. The voltage drops are namely equal across the primary and secondary windings which have the same number of winding turns and the capacity to ground is supposed to be uniformly distributed along the conductor in the same way as in FIG. 3. A voltage symmetrical to ground will thus be obtained in the same way as in the arrangement according to FIG. 3. The supplying circuit will however in the arrangement according to the invention be high ohmic inconsequence of which the oppositely directed current appearing in the matrix wire in the arrangement according to FIG. 3 at the beginning of the pulse is eliminated. The arrangement according to the invention thus reduces the overshoot amplitude to the same extent as the arrangement according to FIG. 3 and can furthermore be used when the pulses are of an alternating polarity.

It is of course possible to connect a number of arrangements according to FIG. 4 in series, as can be seen in FIG. 5 in order to provide a division of the voltage drop across the matrix wires. The disadvantage of such an arrangement is that the voltages in the differential transformers T1, T2, T3 are gradually decreasing. Apparently the voltage drop across the windings in the transformer T1 is 5U/6, in transformer T2 3U/ 6 and in transformer T3 U/6. This makes an optimal dimensioning of the transformers difficult as the number of the Winding turns must be proportional to the voltage drop of the respective winding.

In order to solve this problem a modification of the invention is suggested at which when a division of a matrix wire into a number of sections is wanted, one differential transformer is used in the same way as in FIG. 4 While the other transformers are connected between the sections for example as shown in FIG. 6 where the transformers consist of toroidal cores Ql-Q4. In this way the matrix wire and the number of cores is divided into five equal sections. According to the example each section is supposed to be so small that the voltage drop across the section makes it possible for the toroidal core having only one winding turn to work as a differential transformer. The conditions are shown by means of FIG. 7 which shows the voltage along the matrix wire. As is obvious from FIG. 7 the voltage at the terminals connected to the differential transformer T are +U2 and U respectively. In correspondence to the voltage drop between the points 2c and 2d caused by the voltage drop in the joining matrix wire sections 0-2c and 2d0 respectively the voltage drop U/S appears between the points 2a and 2d. Between the points lb-la the voltage drop U/S appears in a corresponding way in correspondence to the voltage drop between the points 10 and 1d caused by the voltage drop in the conductor sections 0-10 and 1d-0. The corresponding conditions are at toroidal cores Q3 and Q4. As is obvious from FIG. 7 each section obtains a voltage symmetrical to ground which is one fifth of the total voltage and the voltages across the toroidal cores working as differential transformers are equal.

I claim:

1. In a magnetic core matrix, the combination comprising one continuous matrix wire, a plurality of magnetic core elements electromagnetically coupled to said matrix wire, a transformer having a primary winding and a secondary winding, said windings being wound in the same direction, a current pulse source connected to one terminal of said primary winding, a reference potential source connected to a corresponding terminal of said secondary winding, first bilateral current conducting means connecting one end of said continuous matrix wire to the other end of said primary winding and second bilateral current conducting means connecting the other end of said continuous matrix wire to the corresponding other end of said secondary winding whereby current can flow between said primary and secondary windings via only said continuous matrix wire.

2. The combination of claim 1 wherein said current pulse source emits current pulses of both polarities.

3. The combination of claim 1 further comprising a number n of differential connected transformers, the primary and secondary windings of which have the same number of winding turns of said continuous matrix wire, said continuous matrix wire forming a loop in such a way that the loop is divided into n+1 sections, within each section there being two segments of said continuous matrix wire which run in two opposite directions, each of said sections containing a number of magnetic core elements through which only one segment of the matrix wire running in one direction passes only once, so that the voltage appearing at a differential transformer because of the voltage drop in that segment of the adjoining sections which passes through the magnetic core elements causes an equal oppositely directed voltage drop in the other segment of said sections.

References Cited UNITED STATES PATENTS 3,409,883 11/1968 Norton 340-174 STANLEY M. URYNOWICZ, JR., Primary Examiner 

